Initial Results

Paul Miara, DDS*

In the 1970s, chemical bleaching techniques that utilized heat-
and light-activated hydrogen peroxide were reintroduced for the treatment of
tooth discoloration caused by new tetracycline antibiotics,1 which
has since become a recurring clinical concern.2-4 Researchers first
described the catastrophic effects of tetracycline on tooth color in the 1960s.
The treatment of these patients with bleaching methods has been described in
various publications.5,6

Numerous investigations have been conducted to improve this
chemical treatment and clearly define the clinical procedures and their field
of application.7,8 These studies were often predicated on the use of
35% hydrogen peroxide, activated by a halogen lamp.9 Nevertheless,
other studies that use highly concentrated (70%) solutions have been identified
(eg, Zaragoza Bleaching Method),10,11 where the use of hydrogen
peroxide is activated only by heat (Figure 1). These techniques have been
evaluated since the beginning of the 1980s, and many remain popular methods for
treating stained dentition.12

Despite the use of highly concentrated bleaching solutions,
preliminary treatments, powerful lamps, and dangerously high temperatures, the
results of tooth-whitening procedures remain limited. Recent developments in
chairside bleaching agents, which advocate the use of highly concentrated gels,
chemical accelerators, plasma/laser high-energy lamps, and light-cured gingival
barriers, have subsequently simplified these treatments. Although the results
achieved with these methods have demonstrated a slight improvement, they are
not significantly different from those currently obtained with at-home
bleaching techniques, and further amelioration is necessary.

In 1989, the use of a 10% carbamide peroxide gel (equivalent to
3.6% of H202) was proposed.13,14 The bleaching
gel was applied via a plastic tray and worn for one to eight hours each day for
two to six weeks.15,16 This technique proved to be a simple, rapid,
inexpensive, and efficient modality that presented minimal risk to the existing
tooth structure.17

At-home bleaching currently has well-defined indications and
limitations,18 and is efficacious primarily for nonpathological
staining (eg, unvarying yellow and orange discolorations). In instances where
pathological staining (eg, gray band) is present, a prolonged chairside
treatment or the use of a more concentrated gel is required, although the
desired results may not be achieved.19 Due to the caustic nature of
tooth-whitening agents with higher chemical concentration, many bleaching
formulations must be administered chairside to prevent tissue damage.20,21
In order to activate these agents and to obtain their decomposition reaction, a
halogen, plasma, or even laser light-source is required.

The decomposition reaction of some bleaching formulations can be
initiated with a light source or a chemical accelerator, which results in the
formation of oxidizing ions (Figure 2). Two reactions have become generally
accepted:

Photo dissociation

(light, temperature)

2H2O2 ----- 2H2O + O2

Anionic dissociation

(Basic Ph + activator [perborate or persulfate])

temperature

H2O2 ----- HO2- + H+

The carbamide peroxide decomposition reaction also results in the
formation of oxidizing ions.

10% carbamide peroxide ----- 6.4% urea + 3.6% H2O2

-----water and oxygen ions

Once initiation has occurred, either photo dissociation or anionic
dissociation may occur. According to other researchers,19 a third
reaction may occur in which a combination of the first and second reactions
result in the formation of more reactive oxygen ions and HO2 free
radicals. The carbamide peroxide decomposition reaction also results in the
formation of oxidizing ions.

Selection
of an Optimal Bleaching Modality

For years, clinicians have been unable to explain why the use of
low levels of hydrogen peroxide (2% to 4%) in at-home bleaching techniques is
more effective than higher concentrations (30% to 50%) utilized in a chairside
procedure. Why has no dental researcher, author, or manufacturer provided a
logical explanation for this clinical experience, which is well-known among
clinicians? While the duration of application is often cited as a paramount
factor, this is not the sole explanation for this circumstance.

At-Home
Bleaching

As carbamide peroxide is activated within a bleaching tray, slight
pressure is created by the release of the bleaching agent (Figure 3). The
gradual decomposition of the carbamide gels allows this pressure to be
maintained for several hours, during which time oxygen ions are able to
permeate the enamel due to their light molecular weight. The high viscosity of
the carbamide peroxide gels and the seal of the bleaching tray maintain this
pressure, which is essential for the permeation of the oxidizing molecules. In
order to enhance the seal of an at-home bleaching tray, it should be trimmed
horizontally 2 mm to 3 mm from the neck of the teeth.

Chairside
Bleaching

Following the placement of a gingival barrier, a hydrogen peroxide
gel or liquid is applied to the discolored teeth and activated with heat,
light, or a chemical agent (eg, sodium perborate).9,21 Once the
decomposition reaction is initiated, small bubbles appear in the gel that
indicate the release of the oxygen ion. Unlike the at-home bleaching technique,
these ions migrate and only a small proportion of them will permeate the enamel
(Figure 4). In order to enable the permeation of oxidizing ions through the
enamel, the nascent oxygen must be guided under pressure. For an understanding
of this phenomenon, it is necessary to review the action mechanism of
treatments used for discolored nonvital teeth.

For more than a decade,22 clinicians have used a
blending mixture of sodium perborate and distilled water, which yields fewer
oxygen ions than does hydrogen or carbamide peroxide.23 Despite a
low release of oxygen ions, this technique is very efficient and presents
minimal risk.18,24 This has been attributed to the provision of a
perfect seal on two sides of the pulp chamber (Figure 5). The increase in
pressure confined to a perfectly sealed small cavity facilitates the permeation
of the oxygen ions from the pulp chamber into the dentin and enamel.25

This action mechanism is considered to be a conventional method,22
and it has been noted that if the zinc-eugenol provisional cement does not
yield a perfect seal, the sodium perborate will have little or no effect. As a
result, the clinicians found it necessary to place the bleaching agent under
pressure during its decomposition in an effort to force the oxidizing ions to
permeate through the dentin enamel. Following a myriad of trials involving a
modified home bleaching tray,26 a protocol termed "the
compressive bleaching technique" has been developed.

(Continued from page 1 )

Case
Presentations

Case
1

A 25-year-old female patient presented with pathologically
discolored teeth caused by the administration of tetracycline during infancy
(Figure 6). During anamnesis it was determined that previous attempts at
whitening had yielded unsatisfactory results. Although the placement of ceramic
laminate veneers was proposed, the patient declined this suggestion and elected
to first undergo a bleaching protocol using chemical means; the results of the
whitening would determine if prosthodontics were necessary.

A combined technique was selected for this patient utilizing a
conventional home bleaching technique that contained a 10% carbamide peroxide
gel, as well as a highly concentrated hydrogen peroxide gel (35%) that was
applied chairside with the compressive technique. During the initial
appointment, the initial color of the patient's teeth was assessed (shade C3) using
a shade guide (Figure 7). In order to fabricate two sets of trays - one for the
home bleaching modality and the other for the compressive procedure - the teeth
were carefully scaled, and two impressions were made.

To facilitate the home bleaching technique, reservoirs were created
using a light-cured resin; these reservoirs covered the facial aspect of the
teeth and were placed in close proximity to the gingival margins and incisal
edges. In order to prevent the tray from irritating the interproximal spaces,
they were protected with the light-cured resin (Figure 8). The tray was trimmed
at a distance of 2 mm to 3 mm from the gingival margins without scalloped
margins, in order to simplify the trimming and to enhance the fit of the tray
on the edges (Figure 9).

The trays used in the compressive technique were also trimmed
without scalloped margins and are 2 mm to 3 mm shorter; their edges extend to
the gingival margins of the teeth. Their reservoirs are larger and cover all
the facial aspects of the teeth including the incisal edges, and are 2 mm from
the gingival margin (Figure 10). In addition, the interproximal spaces are
protected to avoid a malposition of the tray following placement of gingival
protection. Since it is difficult to protect the gingival region and close the
trays beyond the premolars, the trays should not be extended beyond the first
premolar or first molar.

Chairside
Protocol

In order to remove any soft deposit, the teeth were first cleaned
with an air polisher. The use of an automatic retractor was indispensable for
completing this procedure. The trays were then tried in and adjusted. Gingival
protection facilitated for the maxilla and mandible with a light-cured resin
barrier (Figure 11). Once the teeth were recleansed and rinsed, the tray was
reseated (Figure 12), the reservoirs were filled with 35% hydrogen peroxide
gel, and any excess was removed. Each tray was sealed along the facial and
lingual edges with light-cured resin material to prevent any leakage during gel
decomposition (Figure 13). Once the facial and lingual edges of the tray were
sealed (Figures 14 and 15), the gel was activated with a halogen or plasma lamp
(Figure 16). Each of the four chairside appointments was approximately 30
minutes in duration (Figure 17). Between these visits, the patient was
instructed to apply the 10% hydrogen peroxide gel nightly with the home
bleaching trays for 20 consecutive days.

During the course of treatment, the patient experienced slight
sensitivities to heat and cold. Although all the discolorations did not
disappear entirely, the shade of the teeth changed from shade C3 to shade A0
(Figure 18). The patient was pleased with the aesthetic result of the whitening
procedure, and the prosthetic treatment was unnecessary. It is important to
note that a fluoride treatment should be advised for several days in order to
facilitate surface remineralization while reducing hot and cold sensitivities.27
The fluoride regimen, in this instance, required the patient to wear trays
filled with fluoride gel for two to three hours each day.

Case
2

A 30-year-old female patient presented with nonpathological yellow
and orange discolorations and requested whitening treatment (Figure 19).
Following anamnesis and complete clinical examination, a tooth-whitening
treatment was planned for the patient. Since she declined to wear trays at
night, chairside treatment using the compression technique was administered.

Prior to treatment, the initial shade of the teeth was recorded
and determined to be A3.5. Trays were fabricated in accordance with the
aforementioned protocol, and the compressive technique was utilized. The goal
to reach shade A1 following three or four 30-minute treatments was accomplished
(Figures 20-21-22), as this specific bleaching technique was effective on
this type of discoloration. The patient was pleased with the aesthetic
enhancement achieved through the use of this technique.

Current
Clinical Investigations

The author's initial clinical results were determined through
treatment of more than 40 patients in the first year. Thus far, the clinical
results appear to be promising, and these cases will be continuously monitored
to determine the long-term success of the compressive technique. Two additional
investigations are currently in progress that should soon provide scientific
documentation of the technique's efficacy. The first is a comparative study
realized by three clinicians; the second is an in vitro study to examine the
volume and speed of the permeation of the oxygen ions through the enamel with
and without compression. The results of these investigations will be presented
as these data become available.

Conclusion

The basic principle of chemical bleaching is characterized by the
permeation of oxygen ions through the enamel and the dentin of discolored
teeth. In order to obtain an effective permeation under the best conditions, it
is necessary to use the compressive technique with either the at-home or
chairside modality. The compressive bleaching technique described in this article
has been clinically tested repeatedly and is now clearly defined. It can be
used with several high concentration gels, as they can be quickly decomposed
using light or a chemical agent. Although the compressive bleaching technique
makes it possible to obtain better results than the conventional technique, it
cannot claim to treat all kinds of dental discolorations. Further progress is
necessary to enhance the permeation and efficiency of current products.